1. Field of the Invention
The present invention relates to a microwave phase shifter and more especially a millimeter-wave phase shifter containing a dielectric waveguide, a conductor reflector plane parallel to one of sides of the waveguide and piezoelectric means for adjusting the distance between the reflector plane nd the waveguide.
Apart from a dielectric waveguide phase shifter with piezoelectric control, the invention concerns dielectric waveguide and variable radiation pattern or lobe scanning antennae, in which the phase shifter contains periodical perturbations.
2. Description of the Prior Art
The article "Electronic Phase Shifter for Millimeter-Wave Semiconductor Dielectric Integrated Circuits" by Harold JACOBS and Metro M. CHREPTA, IEEE, transactions on microwave theory and techniques, Vol. MTT-22, No. 4, April 1974, pages 411 to 417, establishes that the presence of a metal plane placed on an upper side of a dielectric guide transforms this latter into an image guide. This article discloses an approximate calculation by the MARCATILI method to evaluate the propagation constant in the guide in the two extreme conditions: totally dielectric guide when the conductor plane is infinitely remote, and an image guide when the conductor plane is directly placed on one side of the guide. No calculation is made in this article on the general case, showing the variation in the propagation constant in the guide as a function of the distance of the conductor plane to the dielectric guide side.
An attempt has been made to obtain a variation in the propagation constant via an electronic control using strips of p-i-n diodes spaced regularly apart and integrated on one side of the dielectric waveguide. When the diodes are forward-biased, the intrinsic regions of the p-i-n diodes behave as a conductor plane, and when the diodes are reverse-biased, i.e. do not conduct, they simulate a state in which no conductor plane is present. Dielectric waveguide devices and p-i-n diode strips have been described in the aforesaid article and in the article "Metal Walls In Close Proximity to a Dielectric Waveguide Antenna" by Kenneth L. KLOHN, IEEE transactions on microwave theory and techniques, Vol. MTT-29, No. 9, September 1981, pages 962-966.
The principle consisting in simulating the presence or absence of a conductor plane by p-i-n diodes is theoretically a good one. Nevertheless, in practice, despite the injection of carriers in the intrinsic region of the diodes, the diodes do not perfectly conduct especially with millimeter-waves. This explains the disappointing result obtained with these phase shifters such as a phase shifting limited to 35.degree./cm at 70 GHz. Moreover this type of phase shifter cannot be used to create a continuously variable phase shift. In fact, for low diode biases implying a little phase shift, the intrinsic region behaves like a dielectric with very heavy losses.